Pygmy dipole strength in86Kr and systematics ofN=50isotones

Abstract

The dipole strength of the $N=50$ nucleus ${}^{86}$Kr was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 7.9 and 11.2 MeV delivered by the linear accelerator ELBE as well as using quasimonoenergetic and linearly polarized $\ensuremath{\gamma}$ rays of 10 energies within the range from 4.7 to 9.3 MeV delivered by the HI$\ensuremath{\gamma}$S facility. A high-pressure gas target was used. We identified 39 levels up to an excitation energy of 10.1 MeV. Simulations of $\ensuremath{\gamma}$-ray cascades were performed to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross section derived in this way up to the neutron-separation energy is combined with the photoabsorption cross section obtained from a $(\ensuremath{\gamma},n)$ experiment at HI$\ensuremath{\gamma}$S. The enhanced $E1$ strength found in the range from 6 to 10 MeV is compared with the ones in the $N$ $=$ 50 isotones ${}^{88}$Sr, ${}^{90}$Zr, and ${}^{92}$Mo and with predictions of calculations within the quasiparticle-phonon model.